1. Field of the Invention
This invention relates to the separation and recovery of active catalyst particles from spent or used catalyst particles having carbonaceous, sulfur and metallic deposits thereon by an air elutriation process. In another aspect of this invention, the used catalyst particles or the recovered active catalyst particles are additionally regenerated by burnoff of the carbon and sulfur deposits under controlled conditions in the presence of an oxygen-containing gas. This regeneration step may be preceded or followed, if desired, by a rejuvenation step in which a part, or substantially all, of the metallic deposits are removed. The active catalyst particles recovered can be recycled to a catalytic reactor, such as an H-Oil.RTM. reactor of a hydrotreating process system.
During catalytic reaction processes, as exemplified by, for example, hydrotreating processes utilizing ebullated-bed reactors, the catalysts employed gradually are deactivated by virtue of various metallic elements such as vanadium, nickel, etc. being deposited thereon and by virtue of an accumulation of carbonaceous deposits on the catalyst particles. The catalyst bed in an ebullated-bed reactor from which periodic or continuous withdrawal of portions of used catalyst and replacement of the withdrawn material with fresh catalyst is carried out the catalyst bed will contain particles which have been in the reactor for widely different periods of time. As a result, in the ebullated-bed reactor operating with periodic or continuous catalyst replacement at any given time different particles of the catalyst have widely varying amounts of deposited metals thereon and carbonaceous deposits. Particles which have been in the reactor for only a short time have a relatively low metals content and such particles still have a relatively high catalytic activity but such high activity particles are discarded in the catalyst withdrawals. Also, as the catalyst particles remain in the reactor there is a tendency of the longer catalyst extrudate particles to break thus forming shorter catalyst particles and through attrition of the catalyst under continued usage an increase in the amount of catalyst fines result which are known to contain an increased concentration of metals as compared to the longer catalyst particles.
There has been a need in the art for a practical method for conveniently recovering relatively high activity catalyst particles from spent hydrotreating catalyst withdrawn from a fluidized-bed catalyst reactor system, such as ebullated-bed or continuous-stirred-tank reactors utilized in processing high sulfur and metals-containing hydrocarbon residuum feedstocks.
2. Prior Art
Canadian Patent No. 1,159,402 discloses a process for the recovery of used contaminated catalyst according to Particle density differences by fluidization in light liquid hydrocarbon fractions boiling in the range of 200.degree. to 450.degree. F., such as light naphtha, kerosene, fuel oil or water. In this process which is suitable for treating used catalyst derived from fluidized- or ebullated-bed reactor systems such as H-Oil.RTM., involving continuous or periodic withdrawal of portions of used catalyst and their replacement with fresh catalyst low density and high density fractions of used catalyst are produced. The low density fractions of used catalyst may be regenerated by carbon burnoff after removal from the light-hydrocarbon-fluidization unit and before being returned to the reactor. The high density fraction of used catalyst is, optionally, processed for recovery of deposited metals.
U.S. Pat. No. 3,809,644 discloses a process for multiple stage hydrodesulfurization of high sulfur, metals-containing petroleum residuum stocks in a multiple stage ebullated-bed hydrogenation process where catalyst used in the final stage reaction zone is removed and introduced without any additional treatment such as carbon burnoff, etc. to the preceding reaction zone thus extending the activity and effective life of the catalyst. In this process all fresh make-up hydrogen for the process is injected into the final reaction zone so that the hydrogen sulfide in the gas leaving that reaction zone is maintained below about three mole percent, thus substantially improving the desulfurization reaction rate in that reactor. The partially deactivated catalyst backstaged from the final reactor becomes guard-type contact solids for metals removal in the preceding stage reactor or reactors. Metals removal from the residual feedstocks can be maintained at the desired level without using high reaction temperatures. This process is reported to be especially effective when three reaction zones connected in series are employed and is applicable for producing low sulfur fuel oil from feedstocks containing 2-5 weight percent sulfur and having metals content ranging from about 20 p.p.m. vanadium to as much as 600 p.p.m. vanadium.
U.S. Pat. No. 4,621,069 discloses a process for effective regeneration of used catalyst to remove deposited carbon and sulfur compounds by staged controlled burnoff and in this process the burnoff is accomplished by staged burnoff in multiple zones wherein the used particulate catalyst is introduced into a first zone where the catalyst is contacted at 300.degree.-500.degree. F. with an inert gas for 1-2 hours residence time to evaporate liquid components from the catalyst; the oil-free catalyst is then passed to a second zone wherein the catalyst in a thin bed is contacted at 780.degree.-800.degree. F. with a gas containing 0.5 to 1.0 V % oxygen in an inert gas for 4-6 hours residence time; the partially regenerated catalyst is passed to a third zone where the catalyst in a thin bed is contacted with a gas containing 1-2 V % oxygen in an inert gas at a temperature of 800.degree.-850.degree. F. for 4-6 hours residence time and finally the further regenerated catalyst is passed to a fourth zone where the catalyst is contacted at 800.degree.-850.degree. F. with a gas containing 2-6 V % oxygen in an inert gas for 6-10 hours residence time to complete burnoff of carbon and sulfur deposits from the catalyst.
U.S. Pat. No. 4,720,473 discloses a process for treating a spent hydrotreating catalyst having an L/D greater than one by (1) stripping volatilizable hydrocarbons to form free-flowing catalyst particles, (2) passing the free-flowing catalyst particles to a rotating drum length grading unit having indentations in the cylindrical wall where the catalyst particles with a length less than L.sub.1 are separated from the desired catalyst particles having a length greater than L.sub.1 comprising lightly contaminated particles and more heavily contaminated catalyst particles (Product A), (3) passing the Product A to a density grading unit utilizing gas suspension on a vibrating air table wherein the lightly metals contaminated catalyst particles are separated from Product A.
In this density grading step the lightly metals contaminated catalyst particles become suspended in a gas above the more heavily metals contaminated catalyst particles, the more heavily metals contaminated particles are caused to move upwardly along an inclined vibrating surface and are collected at a first density grading unit outlet, the lightly contaminated catalyst particles which contact a lower portion of the vibrating surface are collected at a second density grading unit outlet. In a final step the lightly metals contaminated catalyst particles are passed to a regeneration zone in which carbonaceous deposits are removed in a controlled burnoff in the presence of an oxygen-containing inert gas at a temperature of about 200.degree. to 700.degree. C. Alternatively, the lightly-contaminated catalyst particles from the density grading zone can be passed to a rejuvenation zone where the catalyst particles are acid leached to remove undesired metals from the catalyst particles which are then passed to a regeneration zone.
U.S. Pat. No. 4,454,240 discloses a catalyst regeneration process which includes a metal contaminants removal step. This procedure is particularly useful for recovering used catalyst from fluidized-bed catalytic reaction systems such as H-Oil.RTM. and H-Coal.RTM. hydrogenation processes using ebullated-bed reactors, from fixed-bed catalytic reaction systems, and also from fluid catalytic cracking (FCC) processes. Preferred feedstocks for the reactor processes are from petroleum and coal. Catalyst having contaminant metals removed and regenerated by this process is said to have activity essentially equal to fresh catalyst. In the process of this patent the used catalysts are first washed with a hydrocarbon solvent such as naphtha, toluene and mixtures thereof, etc. to remove process oils; the oil-free catalyst is then contacted for at least 5 minutes with an aqueous solution of sulfuric acid and an ammonium ion at a temperature of from 60.degree.-250.degree. F. which converts the metal contaminants to the respective soluble sulfate compounds; the metals-laden solution is drained off; the treated catalyst is washed with water to remove the residual aqueous solution and, in a final step, the washed, treated catalyst is subjected to a carbon burnoff in which the catalyst is contacted with a 1-6 V % oxygen in an inert gas mixture to remove carbon deposits.
U.S. Pat. No. 4,325,818 discloses a dual solvent refining process for solvent refining petroleum based lubricating oil stocks with N-methyl-2-pyrrolidone as a selective solvent for aromatic oils where a highly paraffinic oil having a narrow boiling range approximating the boiling point of N-methyl-2-pyrrolidone is employed as a backwash solvent.
U.S. Pat. No. 4,311,583 discloses a solvent refining process utilizing N-methyl-2-pyrrolidone as solvent in which primary extract is cooled to form a secondary raffinate and secondary extract and the secondary and primary raffinates are blended to produce an increased yield of product of desired quality.
U.S. Pat. No. 4,057,491 discloses a process for recovering N-methyl-2-pyrrolidone from the raffinate and extract phases produced by its use in hydrocarbon extraction processes such as in a lube oil extraction process.
Guillen et al., in a paper entitled, "Study of the Effectiveness of 27 Organic Solvents in the Extraction of Coal Tar Pitches" (Energy and Fuels, 1991, Vol. 5, pp. 192-204) disclose a study of the extractive ability of organic solvents including 2-pyrrolidone, N-methyl-2-pyrrolidone, etc. on coal tar pitches.